Drug companies that had medicines tested by contractor Cetero Research might have to reevaluate results, U.S. regulators warned after the firm was found faking documents and manipulating samples. The Food and Drug Administration said on Tuesday two 2010 inspections, an internal company investigation and a third-party audit uncovered "significant instances of misconduct and violations" at a Cetero facility in Houston. The Cary, North Carolina-based firm does early-phase clinical research and bioanalytics for a number of drugmakers. The pharmaceutical companies can then use those studies as supporting evidence in drug approval applications to the FDA.